Optical fiber gratings are used for spectral shaping in modem telecommunications systems and sensing systems. A typical optical fiber grating includes a periodic or quasiperiodic pattern of refractive index fluctuations or perturbations along an optical fiber. Bragg-based fiber gratings reflect light within a narrow wavelength band and transmit wavelengths of light outside of that band to provide spectral shaping. Long period fiber grating designs couple selected wavelengths of light from the fundamental mode into rapidly attenuated cladding modes to provide spectral shaping. These spectral shaping properties permit fiber gratings to be used as gain equalizers, narrowband filters, dispersion compensators, and shift detectors.
Spectral shaping can also be accomplished with tapered optical fibers. For example, U.S. Pat. No. 5,473,714 issued to Vengsarkar on Dec. 5, 1995, titled "Optical Fiber System Using Tapered Fiber Devices", discloses a tapered fiber device which can be used for optical filtering. The taper of the fiber is dimensioned to permit signals of a first wavelength to pass with little loss while signals of a second wavelength are blocked.
Telecommunications and sensing systems operate under many conditions which cause them to experience spectral changes. Unfortunately, conventional fiber gratings and tapered fibers have static spectral shaping properties which can not be tuned or adjusted to compensate for these changes. Therefore, there is a need for an optical fiber device that can be adjusted or tuned to provide different spectral shaping properties.